Concern over environmental pollution has been growing over the recent decades. One pollution source attracting the attention of the environmental movement is the service station that dispenses motor vehicle fuels. These stations contribute to the pollution of the environment in several ways, including spilling of fuel during the filling of a motor vehicle fuel tank and escaping fuel vapors.
To combat the overfilling problem, the fuel dispensing nozzles normally incorporate an automatic shutoff mechanism to terminate the flow of fuel through the nozzle. This mechanism is responsive to the filling of a receiving tank to a point near its top so as to trip a valve operating lever and thereby discontinue fuel flow. The automatic shutoff mechanisms now in use commonly utilize a pressure-sensitive diaphragm that is shifted by the creation of a suction effect on one side thereof. The suction is created by the flow of fuel past an aspirating passage after an air pickup tube near the outlet end of the dispensing nozzle has been covered with liquid as it rises near the top of the receiving tank. The shifting of the diaphragm trips the automatic shutoff mechanism to close a main flow control valve in the nozzle. Such an automatic shutoff arrangement for a fuel dispensing nozzle is shown in U.S. Pat. No. 2,528,747.
Fuel dispensing nozzles normally have an elongated discharge nozzle that extends downwardly into the fuel tank of a vehicle and that has an air intake port located near the outer end of the nozzle. Since the discharge nozzle extends into a fuel tank a considerable distance, the flow of fuel into the gasoline tank will be automatically terminated by pressure-actuated shutoff mechanisms of the aforesaid type when the fuel level approaches the top of the tank and covers the air inlet on the nozzle.
This type of nozzle creates a venturi effect in the air pick-up tube and syphons the gases in the tank through the tube and back into the fluid flow within the nozzle through the previously mentioned aspirating passage. Consequently, the fluid is being continuously aerated during the tank filling. When the fluid exiting the nozzle strikes the fluid in the tank, foaming occurs, and the gases in the fuel are released. The result in the release of additional vapors and an increase in the gas pressure within the tank. While some of the pressure is relieved by the syphoning effect of the breather tube, a large volume of gas is vented through the filler neck of the tank into the atmosphere, resulting in harmful pollution of the atmosphere initially, and ultimately of the ground and water. The automatic shut-off mechanism of the present day fluid dispensing nozzles thus solve one pollution problem but contribute to another one by aerating the fuel prior to its delivery into the tank thereby increasing the amount of fuel vapor vented to the atmosphere.
Another problem with modern nozzles and the aerated fuel they deliver is that the foaming of the fuel in the tank of a motor vehicle can itself trigger the automatic shut-off, resulting in the tank not being filled to capacity. This problem is exacerbated when the fuel being dispensed is diesel fuel rather than gasoline since diesel fuel foams much more readily than gasoline and thus will likely trigger the automatic shut-off mechanism even more prematurely than a gasoline dispensing nozzle would. The nozzle operator must then wait for the foam to subside to continue to fill the tank or must continuously manually operate the main operating lever of the nozzle to obtain the additional fuel flow required to fill the tank since the operating lever will be tripped to a closed position shortly after it is actuated. This results in additional wear and tear on the nozzle and fluid pumps in addition to wasting the time of the nozzle operator.
It would be desirable, therefore, to have a fluid dispensing nozzle that had an automatic shut-off mechanism but that did not aerate the fluid prior to tank delivery, thereby minimizing environmental pollution and economic losses otherwise due to aeration of the dispensed fluid.